Drawing on social cognitive theory, three main research objectives have been addressed. In the first instance, we examined the relationship between parental proviolence attitudes and aggressive behaviour in preschool children. Secondly, we analysed the relationship between parental moral disengagement and aggressive behaviour in preschool children. Third and finally, we evaluated the moderating role of teacher–child closeness in the relationship between family variables and aggressive behaviour in preschoolers. Using a sample of 388 children (47.2% girls, 52.8% boys), mothers and fathers rated their own proviolence attitudes and propensity to morally disengage. Teachers completed a questionnaire to rate their closeness to each student in their class. Four months later, the teachers in each participating class were asked to provide ratings of overt and relational aggression for each participating child. Hierarchical regression analyses showed a positive significant relationship between maternal proviolence attitudes, both maternal and paternal moral disengagement and overt aggression in preschool children, but no relationship was found for relational aggression. It was also found that medium/high teacher–child closeness moderated the relationship between parental proviolence attitudes, parental moral disengagement, and overt aggressive behaviour in children, but only in the case of mothers.